The present application relates to a non-aqueous electrolyte battery and, more particularly, to a non-aqueous electrolyte battery having a microporous separator.
Owing to the remarkable development of a recent portable electronic technique, cellular phones and notebook-sized computers have been recognized as fundamental techniques which support a society of highly advanced information technologies. Further, studies and development regarding the realization of advanced functions of those apparatuses are vigorously being made. Electric power consumption of those apparatuses is also increasing more and more in proportion to them. On the other hand, it is demanded that those electronic apparatuses can be driven for a long time. Inevitably, it is demanded to realize a high energy density of a secondary battery as a driving power source.
The higher energy density of the battery is preferable from viewpoints of an occupation volume, a weight, and the like of the battery built in the electronic apparatus. At present, since a lithium ion secondary battery has an excellent energy density, such a battery has been built in most of the apparatuses.
Ordinarily, in the lithium ion secondary battery, a lithium cobalt acid is used for a cathode, a carbon material is used for an anode, and the battery is used at an operating voltage within a range from 2.5V to 4.2V. In a unit cell, a terminal voltage can be raised to 4.2V owing to excellent electrochemical stability of a non-aqueous electrolyte material, a separator, or the like.
At present, in the lithium ion secondary battery which operates at maximum 4.2V, a cathode active material such as a lithium cobalt acid or the like which is used in such a battery merely uses a capacitance of about 60% of its theoretical capacitance. In principle, a residual capacitance can be utilized by further raising a charge voltage. Actually, for example, as disclosed in Patent Document 1 (International Publication No. 03/019713), it has been known that the high energy density can be realized by setting the voltage upon charging to 4.25V or more.
However, similar non-aqueous electrolyte batteries have been examined and is has been found out that the following “problem peculiar to the battery system” exists in the battery. That is, when the charge voltage is set to a value over 4.2V, particularly, an oxidation atmosphere near the cathode surface is enhanced, so that a non-aqueous electrolyte material or a separator which is physically come into contact with the cathode is liable to be subjected to oxidation decomposition. Eventually, a resistance in the battery increases and, particularly, high-temperature characteristics or the like deteriorate.
In the case of a battery whose charge voltage has been set to a value over 4.2V, since a risk caused by a wrong using method is larger than that in the case of a battery in the related art, it is necessary to further improve safety.